Gas turbine engines with can annular combustion arrangements have compressors that deliver compressed air to the combustion arrangement. The compressed air exits the compressor through a diffuser and enters a plenum from which the combustion arrangement draws the compressed air. The plenum is bounded on an outside by a combustion section casing. A top hat arrangement including a plurality of top hats and associated portals may be used as part of the combustion section casing. Top hat arrangements provide discrete radially extending chambers that enclose at least portions of respective combustor cans. The discrete combustor cans feed respective and discrete transition ducts which ultimately terminate immediately upstream of a first row of turbine blades of a turbine section. Each top hat arrangement thus forms an outer boundary of a respective annular chamber with an inner boundary formed by a respective combustor can and/or transition duct.
In a typical premix can annular combustor, a pilot burner is centrally disposed in the combustor can and is surrounded by a symmetrically disposed plurality of premix burners. While the structure of the combustor is symmetrical about its flow axis, compressed air entering the combustor can inlet may not be evenly distributed circumferentially due to the convoluted path taken by the air from the compressor to the combustor inlet, and each premix burner may be receiving a different amount of compressed air, yet each premix burner may be delivering the same amount of fuel. Consequently, fuel to air ratios may vary from one premix burner to another. In addition, air entering each burner may have varying local turbulence. Further, these parameters may change with changing power output, and/or changing ambient weather conditions, which vary the density and moisture of air entering the compressor, which effect aerodynamics of the air traveling to the combustor can inlet.
Various approaches have been taken to condition the air entering the combustor can inlet in order to accommodate these factors, such as by using airfoils as disclosed in U.S. Pat. No. 4,129,985 to Kajita et al. However, none of these approaches appears to have completely resolved the problem. As a result, there remains room in the art for improvement.